1. Field of the Invention
The invention generally relates to a method and a numerically controlled orbital machining apparatus for producing a hole in a workpiece by means of a cutting tool rotating about its own tool axis as well as eccentrically (orbiting) about a principal axis corresponding to the longitudinal center axis of the hole to be machined. More particularly, the invention relates to a method and an apparatus for producing a conical hole, or a hole or recess having at least a one conical section, in a workpiece by using a substantially cylindrical cutting tool having a cutting head diameter essentially smaller than the top and bottom diameter of the hole to be formed.
The invention also relates to a method and an apparatus for forming holes in a workpiece, where the wall of said holes have a curved profile, such as holes having convex or concave wall sections.
2. Description of the Related Art
Conventionally, conical holes in a workpiece are produced by the combined action of rotating a conical cutting tool (cutting head) having tapered cutting edges and feeding the tool into the workpiece. Such conical tools must have a shape and dimensions, which accurately correspond to the final dimension of the hole to be drilled. Such conical tools are expensive and may not be reground many times due to diminishing dimensions, which makes the tool quickly useless for further use.
WO 99/62661 discloses an orbital machining apparatus, which is equipped with structural features making it possible to produce conical holes in a workpiece. For this purpose the apparatus comprises a radial offset adjustment mechanism, which may continuously vary the radial offset value (orbiting radius of the tool) while simultaneously rotating the cutting tool about its own center axis and axially feeding the tool into the workpiece. Although conical holes may be produced here by using a substantially cylindrical cutting tool, it is in many instances difficult to obtain a sufficiently fine smoothness of the hole surface.